As generally known in the art, various wireless communication services are provided via wireless communication networks in line with remarkable development of computers, electronics, and communication technologies. The most basic type of a wireless communication service is a voice communication service, which enables wireless voice communication among mobile communication subscribers using their mobile communication terminals regardless of time and place. A wireless data service has recently appeared and enabled mobile communication subscribers on the move to conduct data communication via wireless communication networks with no spatial restrictions.
Therefore, mobile communication subscribers can not only communicate with desired partners at any place and time based on the voice communication service, but also obtain various pieces of daily information (e.g. news, weather, sports, stocks, exchange rates, and traffic) in various types (e.g. texts, voices, and images) based on the wireless data service even on the move.
Meanwhile, a supplementary service for ringback tone alternative service has recently been developed and welcomed by mobile communication subscribers. This service replaces conventional monotonous ringback tones, which are in many cases simple and mechanical sounds (e.g. ringing sounds) generated during call connection and heard by the calling party, with various types of music (e.g. popular songs), recorded voices of the called or calling party, or other types of sounds (e.g. birds singing, water sounds, etc) according to the preference of the called or calling party.
As such, the ringback tone alternative service gives the calling party listening pleasure with various sound sources instead of boredom from monotonous and mechanical ringback tones.
In general, the ringback tone alternative service is available to mobile communication terminals in a mobile communication network based on a mobile communication system, such as CDMA (Code Division Multiple Access) 2000 system or WCDMA (Wideband CDMA) system.
When a mobile communication system provides such a ringback tone substitution service, it commonly uses a voice codec with a variable transmission rate, such as an EVRAC (Enhanced Variable Rate Codec) or an AMR (Adaptive Multiple Rate) codec, in order to improve the efficiency of voice communication and optimize the wireless channel. The voice codec is designed to maximize the channel efficiency so that it can detect speech and silent sections, create a suitable codebook, and provide a voice service at a minimum bit transmission rate by means of mapping.
However, such a voice codec with a variable transmission rate (e.g. EVRC or AMR codec) applies the same logic even for a sound source having few silent sections (e.g. music) and uses a codebook so as to encode the sound source. When a sound source (e.g. music) is mapped onto a voice codebook and coded, the sound source is encoded in conformity with human voice patterns. This means that various patterns appearing in the music are ignored during the encoding process. The resulting coding error degrades the quality of music. Therefore, the voice codec with a variable transmission rate is not suitable for encoding audio-type sound sources, such as music.
In an attempt to solve the problems of voice codecs with a variable transmission rate, it has been proposed and widely adopted in the industry to correct the light source. Particularly, a content provider, who provides sound sources, extracts a sound source from high-quality music (e.g. compact disk), modifies the sound source in conformity with a voice codec (e.g. EVRAC), and encodes the sound source so as to minimize damages to the sound source resulting from the voice codec.
This approach relies on preprocessing based on the characteristics of the EVRAC or manual operation of sound technicians. Although such operations may supplement the quality of EVRAC-based ringback tone alternatives up to the level of voice quality, they cannot provide high-quality ringback tone alternatives.
Meanwhile, it is most efficient to use an audio codec to encode a sound source and provide a ringback tone alternative. However, this requires that a number of technical problems be solved in advance.
Firstly, an audio codec adapted to the voice channel of mobile communication terminals should be used. For example, in the case of the CDMA 2000 system, a voice channel of 8 kbps is used and, in the case of the GSM (Global System for Mobile Communications), a voice channel of 12.3 kbps is used. As such, the audio codec must be modified and adapted to the transmission rate of the voice channel so as to provide ringback tone alternatives with improved quality.
Secondly, the service section needs to be divided into a ringback tone provision section and a voice communication section. An audio codec is used in the former section and a voice codec in the latter section so that a sound source is transmitted to a mobile communication terminal, which then decodes the sound source with a corresponding codec for playback.
Thirdly, a sound source suitable for the audio codec used in the mobile communication terminal and the mobile communication network must be fabricated and provided.
In summary, in order to provide high-quality ringback tone alternatives, it is inevitable to adapt the audio and voice codecs to the ringback tone provision and voice communication sections, respectively, for application to the sound source. In other words, the selection of a codec for a mobile communication network and mobile communication terminals must be based on the service type (e.g. ringback tone substitution service or voice communication service). However, no technology has yet been developed to provide the ringback tone substitution service in this manner.
Even when these technical problems are solved, additional modification or adaptation of various devices in the mobile communication network (e.g. exchangers, base stations, etc) would increase the time, labor, and cost necessary to provide the ringback tone substitution service. This increases the price of the service, affects its quality, and delays the development.